I'm Sayuri Sato, 40 years old. I've been married to my husband for 12 years. We don't have any children, and we live just the two of us. Then, a month ago, my younger sister came to stay with us. Unlike me, my sister is a free-spirited girl who gets totally naked and walks around the room in front of my husband, throwing my daily routine off balance. Recently, I've started to feel like my sister and my husband are getting closer. Just then, I heard my sister's lewd voice coming from the room...